Python: Remove all elements from set using clear() or difference_update() or discard()

In this article we will discuss different ways to remove all elements from a set in python.

Remove all elements from a set using clear() function

In python, the Set class provides a function clear() that can empty a set i.e. delete all elements from the set. For example,

# Create a Set of numbers 
set_of_num = {1, 2, 11, 6, 7, 4, 5, 6} 

# Delete all elements in the set 
set_of_num.clear() 

print('Set Contents: ') 
print(set_of_num)

Output

Set Contents: 
set()

To confirm, if all elements are deleted from the set or not, we can check the size of the set. For example,

# Check the size of list to confirm if all elements are deleted
print('Set Size: ', len(set_of_num))

Output:

Set Size:  0

Remove all elements from a set using difference_update()

In python, the Set class provides a function difference_update() that accepts a sequence as an argument and deletes all the elements in this sequence from the set. Let’s use this to remove all elements of the set,

# Set of numbers
set_of_num = {1, 2, 11, 6, 7, 4, 5, 6}

# Delete all elements of a set from the same set | Empty a set
set_of_num.difference_update(set_of_num)

print('Set Contents: ')
print(set_of_num)

Output:

Set Contents: 
set()

We passed the same set object as an argument in the difference_update(), so it deleted all elements of the set.

To confirm, if all elements are deleted from the set or not, we can check the size of the set. For example,

# Check the size of list to confirm if all elements are deleted
print('Set Size: ', len(set_of_num))

Output:

Set Size:  0

Remove all elements from a set while iterating using for loop and discard()

If we iterate over a set and try to remove each element while iteration, then it will raise error,

# Set of numbers
set_of_num = {1, 2, 11, 6, 7, 4, 5, 6}

# RuntimeError: Set changed size during iteration
for elem in set_of_num:
    set_of_num.discard(elem)

Error

RuntimeError: Set changed size during iteration

It is because we can not modify a set while iterating over it.

So, we will create a list of the set elements, then iterate over that list and for each element, we will delete it from the set,

# Set of numbers
set_of_num = {1, 2, 11, 6, 7, 4, 5, 6}

# Iterate over the elements of set (by converting it to a list)
for elem in list(set_of_num):
    # Remove each element
    set_of_num.discard(elem)

print('Set Contents: ')
print(set_of_num)

Output:

Set Contents: 
set()

To confirm, if all elements are deleted from the set or not, we can check the size of the set. For example,

# Check the size of list to confirm if all elements are deleted
print('Set Size: ', len(set_of_num))

Output:

Set Size:  0

It seems to be an overkill for the small job of just clearing a set, but this solution can be useful if you want to delete some specific elements from the set, while iterating over the set.

The complete example is as follows,

def main():

    print('*** Remove all elements from a set using clear() function ***')

    # Set of numbers
    set_of_num = {1, 2, 11, 6, 7, 4, 5, 6}

    print('Set Contents: ')
    print(set_of_num)

    # Delete all elements in the set
    set_of_num.clear()

    print('Set Contents: ')
    print(set_of_num)

    # Check the size of list to confirm if all elements are deleted
    print('Set Size: ', len(set_of_num))

    print('*** Remove all elements from a set using difference_update() ***')

    # Set of numbers
    set_of_num = {1, 2, 11, 6, 7, 4, 5, 6}

    # Delete all elements of a set from the same set | Empty a set
    set_of_num.difference_update(set_of_num)

    print('Set Contents: ')
    print(set_of_num)

    # Check the size of list to confirm if all elements are deleted
    print('Set Size: ', len(set_of_num))

    print('*** Remove all elements from a set using for loop and discard() ***')

    # Set of numbers
    set_of_num = {1, 2, 11, 6, 7, 4, 5, 6}

    # RuntimeError: Set changed size during iteration
    '''
    for elem in set_of_num:
        set_of_num.discard(elem)
    '''

    # Iterate over the elements of set (by converting it to a list)
    for elem in list(set_of_num):
        # Remove each element
        set_of_num.discard(elem)

    print('Set Contents: ')
    print(set_of_num)

    # Check the size of list to confirm if all elements are deleted
    print('Set Size: ', len(set_of_num))


if __name__ == '__main__':
   main()

Output:

*** Remove all elements from a set using clear() function ***
Set Contents: 
{1, 2, 4, 5, 6, 7, 11}
Set Contents: 
set()
Set Size:  0
*** Remove all elements from a set using difference_update() ***
Set Contents: 
set()
Set Size:  0
*** Remove all elements from a set using for loop and discard() ***
Set Contents: 
set()
Set Size:  0